The present invention is directed generally to air and fluid delivery systems. More particularly, the present invention provides a method and device for an improved motor actuator for controlling dampers or valves used in air or fluid delivery systems. Merely by way of example, the present invention provides techniques for an air duct damper actuator motor including a fan brake configured to produce a braking force when the motor actuator is back driven. But it would be recognized that the invention has a much broader range of applicability. For example the invention can be applied to motor actuators used to control valves in various gas or fluid delivery systems. The invention can also be used to reduce water hammer in water delivery system.
In an HVAC (Heating, Ventilation and Air-Conditioning) system, sometimes referred to as climate control system, extensive ductwork throughout a building is often used to control temperature and humidity of the air within a building. Such duct work is also often used to providing for smoke control, maintaining pressure relationships between spaces, and providing fresh air for occupants. For efficient climate control, electronic duct dampers are often used to shut off air flow to unoccupied or unused rooms, limiting the flow of heated or cooled air to those areas that really need it.
Conventional dampers often are available in two types, normally open dampers and normally closed dampers. Applying power (for example, 24 volts AC at 500 mA) to a normally open damper will cause the damper to close, shutting off all air flow. Conversely, apply power to normally closed dampers causes them to open. A conventional damper often is equipment with a spring, which returns the damper to its original position when power is removed. Dampers are often controlled by a control panel, which sends electrical signals to the damper. Dampers can also be controlled manually by using a switch to apply and remove power to the damper.
Conventional dampers often include valve actuators which are energized for a single direction of rotation and wind up an external spring when they travel in that direction. When power is removed, the external spring back drives the gear train and motor in the opposite direction and returns the valve to the original position. The speeds generated during back driving can often greatly exceed the speeds the motor travels when energized. The inertia that is built up during back drive can damage the gear train after repeated impacts. In water delivery systems using conventional valve actuators, such high speed back drive causes water valves to close quickly, and the sudden interruption in water flow often causes a loud noise commonly known as water hammer. In some conventional actuator motors, a flexible rubber structure has been used as a braking device. In such braking devices, the flexible structure moves radially outward under centrifugal force as the rotational velocity of the motor increases. Such conventional braking devices are often complex and expensive and are often susceptible to reliability problems.
From the above, it is seen that improved techniques for controlling the speed of an actuator motor are desired.